The invention concerns an ultrasonic applicator for ultrasonic scanning, particularly for the purpose of obtaining ultrasonic echo sectional views, such applicator having an ultrasonic transmission and receiving system operable to transmit ultrasonic beam energy so as to scan a desired body region at least in one plane, and utilizing a reflector for the purpose of directing the ultrasonic beam energy along the desired paths for effecting such scanning.
An applicator of this type is prior art from U.S. Pat. No. 3,470,868, for example. The prior art applicator involves a cylindrical parabolic reflector and an ultrasonic transmitting/receiving head arranged for rotation about an axis coincident with the focal line of the reflector, the rotary head assembly also being movable in a longitudinal direction along the focal line. Because of the parabolic contour of the reflector successive pulses of ultrasonic energy which have been emitted from the head assembly toward successive points along such contour are reflected by the latter into a body region which is to be examined along successive parallel beam paths. Thus, during rapid rotation of the ultrasonic head assembly about the focal line, the reflected ultrasonic beam energy scans a body area along mutually parallel lines in each revolution of the head assembly. During corresponding linear imaging of the ultrasonic echo signals, each of which is received from a scanning line in the body area, on the viewing screen of an oscilloscope, a sectional view of the body region which is to be investigated is obtained in the scanning plane. Planes which are parallel to such scanning plane may be imaged by means of a corresponding displacement of the rotating ultrasonic transmitting/receiving head assembly in a direction along the focal line of the parabolic reflector. An additional prior art applicator, which, in a corresponding manner, scans the test object in mutually parallel lines, differs from the applicator as specified by U.S. Pat. No. 3,470,868 in that it contains a rotating deflection mirror in the focal line of the parabolic reflector, instead of a rotating ultrasonic transducer assembly, which rotating mirror serves to initially deflect successive pulses of ultrasonic energy arriving from a stationary transducer into successive incident paths impinging on the parabolic reflector.
Particularly in medical ultrasonic diagnosis, there are body areas of interest which are accessible from the body surface only through relatively narrow acoustic apertures, such as the intermediary spaces between the ribs in the case of heart examinations, for example, or, in the case of skull examinations, thin areas of the bone at specific locations on the skull cap, for example a thin bone area above the ear. Ultrasonic scanning processes which operate according to the principle of sector scanning would be advantageous for such applications since, in this case, the required body surface area which is to be contacted by the applicator for the purpose of transmission of the ultrasonic pulses and reception of the echo signals need correspond only approximately to the area required by the ultrasonic transducer head itself.
In order to carry out a sector scanning in the desired manner, scanning procedures would be conceivable wherein the cyclical displacement of the ultrasonic energy over a desired scanning sector is effected electronically by means of a time sequential excitation of a series of ultrasonic generators which are placed in contact with the body, or a single ultrasonic generator might be mechanically guided, for example by hand, over the body for the purpose of cyclical displacement of the ultrasonic beam. Aside from the fact that the direct coupling of a cyclically scanning sound head to a body surface of a patient, for example, is not unproblematical, and, moreover, that the vibration of the ultrasonic generator on the skin surface can bother the patient, the usual disturbances occurring in connection with a direct coupling of a sound head result. Such disturbances include, for example, multiple echos, which occur between strongly reflecting boundary surfaces of the body and the sound head application surface, and which, as superimposed light points in the ultrasonic echo sectional view, make difficult the diagnostic evaluation of the sectional view. In addition, ambiguities can also result due to minor lobes, and there is the disadvantage of dead zones in the coupling area, since the direct coupling of the strong transmission pulse prevents an echo indication from this close range.
An additional disturbing disadvantage results where the intersecting or focal point of the ultrasonic beam paths is external to, or on, the body surface. If the acoustic aperture is located in the interior of the body, such as the space between ribs, for example, which, in certain circumstances, may be located in the body at a depth of up to several centimeters, the potential advantage of sector scanning would be realized only to a very limited extent.